Epoxy resin with double dynamic bonds cooperatively exchanged and preparation method and application of epoxy resin

Abstract

The invention belongs to the technical field of epoxy resin, and particularly relates to double-dynamic-bond synergistic exchange epoxy resin as well as a preparation method and application thereof. The preparation method of the double dynamic bond synergistic exchange epoxy resin comprises the following steps: adding aromatic dialdehyde and amino-containing disulfide into a solvent for condensation reaction, and filtering and drying to obtain a double dynamic bond curing agent; the preparation method comprises the following steps: adding the double-dynamic-bond curing agent into epoxy resin, carrying out ring-opening addition reaction, carrying out gradient heating curing, and cooling to room temperature, the aromatic dialdehyde is terephthalaldehyde, isophthalaldehyde or o-phthalaldehyde, and the amino-containing disulfide is 2, 2 '-diaminodiphenyl disulfide or 4, 4'-diaminodiphenyl disulfide. The invention designs and synthesizes a double-dynamic covalent bond curing agent containing an imine bond and a disulfide bond, and is used for constructing a novel degradable and self-healing epoxy resin. The material maintains good thermal stability and insulation performance, and realizes degradation and self-healing functions at the same time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of epoxy resin, and particularly relates to an epoxy resin with double dynamic bonds and synergistic exchange, and a preparation method and application thereof. BACKGROUND

[0002] Epoxy resin, as a kind of thermosetting polymer material with excellent performance, is widely used in key fields such as electronic packaging, advanced composites, protective coatings and power insulation due to its outstanding mechanical strength, bonding performance, chemical stability and electrical insulation. Especially in high-voltage electrical equipment, generators, transformers and other major power equipment, epoxy resin is often used as the core material for casting and solid sealing insulation, and its long-term reliability is the basis for ensuring the safe and stable operation of the power grid. However, traditional epoxy resin forms a permanent three-dimensional cross-linked network after curing, which gives it good stability and durability, but local damage such as micro-cracks and scratches caused by external forces or fatigue during use cannot be self-repaired, and damage accumulation will gradually reduce the mechanical and insulation performance, affecting the service life and operation safety of the equipment; the cured epoxy resin product is difficult to degrade and recycle through conventional physical or chemical methods, and most of the waste materials are eventually disposed of by landfill or incineration, not only causing resource waste, but also bringing serious environmental pressure.

[0003] In the prior art, dynamic covalent bonds (ester bonds, disulfide bonds, urea bonds, imine bonds, etc.) are introduced to construct reversible cross-linked networks, which give traditional thermosetting epoxy resin repairable, recyclable, and reworkable properties, while maintaining its excellent thermal stability, mechanical properties and chemical resistance. At present, it has been confirmed that it is feasible to introduce a single type of dynamic covalent bond into the epoxy resin system. For example, based on the dynamic exchange reaction of disulfide bonds, an epoxy resin that can realize damage healing and shape remodeling under heat or light stimulation is developed; based on the dynamic characteristics of imine bonds, the epoxy network can be rapidly dissociated under acidic conditions to realize material degradation. In principle, the introduction of multiple dynamic covalent bonds can achieve multiple functional complementation and synergistic effect. However, the activation energy, response temperature and stimulation method (such as heat, light, and chemicals) of different dynamic bonds differ significantly, making it difficult to achieve synchronous and balanced activation and exchange under the same external conditions, which easily leads to asynchronous network reconstruction and uneven performance. In addition, the introduction of multiple dynamic bonds may affect the electrical performance of the material, such as a decrease in the electrical tree initiation voltage, an increase in partial discharge, and other problems, making it difficult to meet the requirements of power equipment in terms of insulation performance, thermal stability and mechanical properties. SUMMARY

[0004] The purpose of this invention is to provide a dual dynamic bond synergistic exchange epoxy resin, its preparation method, and its application, thereby overcoming the shortcomings of existing technologies. A dual dynamic covalent bond curing agent (IDSE) containing imine and disulfide bonds was designed and synthesized, and used to construct a novel biodegradable, self-healing epoxy resin. This material achieves degradation and self-healing functions while maintaining good thermal stability and insulation properties.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing an epoxy resin with dual dynamic bond synergistic exchange, comprising the following steps: Aromatic dialdehyde and amino-containing disulfide are added to a solvent for condensation reaction, and the double dynamic bond curing agent is obtained by filtration and drying. The double dynamic bond curing agent is added to epoxy resin for ring-opening addition reaction, cured by gradient heating and cooled to room temperature to obtain the final product.

[0006] Among them, the aromatic dialdehydes are terephthalaldehyde, isophthalaldehyde, or o-phthalaldehyde, and the amino-containing disulfides are 2,2'-diaminodiphenyl disulfide or 4,4'-diaminodiphenyl disulfide.

[0007] The present invention discloses a dual dynamic covalent bond curing agent (IDSE) prepared through a one-step condensation reaction. The molecular structure of this IDSE simultaneously contains amino groups capable of ring-opening addition reactions with epoxy groups, dynamic imine bonds, and dynamic disulfide bonds. This curing agent can be used to directly react with epoxy resins to construct a three-dimensional cross-linked network exhibiting synergistic dynamic characteristics of both imine and disulfide bonds. In this epoxy resin cross-linked network, the exchange reactions of imine and disulfide bonds do not occur independently, but rather through a mutually promoting, hierarchical synergistic mechanism. Specifically, under thermal or stress stimulation, disulfide bonds preferentially undergo exchange and recombination, triggering local network topological reconstruction. This creates a more favorable spatial conformation and reaction microenvironment for the exchange of adjacent imine bonds, significantly reducing the overall activation energy barrier for imine bond exchange. This synergistic effect is key to the material's efficient room-temperature self-healing and rapid degradation.

[0008] In some other embodiments, the molar ratio of aromatic dialdehyde to amino-containing disulfide is 1:(1-2); for example, the molar ratio of aromatic dialdehyde to amino-containing disulfide is 1:1, 1:1.05, 1:1.1, 1:1.2, 1:1.5, or 1:2, specifically 1:1 or 1:2. This ratio enables precise synergy between dynamic imine bonds and dynamic disulfide bonds, allowing the aldehyde group and amino group to react completely, forming a stable imine bond network. Simultaneously, the disulfide bond, as a second dynamic crosslinking point, can undergo reversible exchange under stress. This achieves efficient synergy in material repair, stress dissipation, and network reconstruction, ultimately endowing the material with excellent self-healing properties, recyclability, and mechanical toughness.

[0009] The aromatic dialdehyde is terephthalaldehyde, and its amino-containing disulfide is 2,2'-diaminodiphenyl disulfide. Terephthalaldehyde provides a rigid benzene ring skeleton and two aldehyde groups, while 2,2'-diaminodiphenyl disulfide contributes the amino group and dynamic disulfide bonds. When they react in a 1:1 molar ratio, the aldehyde group and amino group completely condense to form an imine bond, while the disulfide bond remains in the polymer network as a second dynamic crosslinking point. This design gives the material both the rapid exchange capability of imine bonds (thermal / water-stimulated response) and the reduction response characteristics of disulfide bonds. Under stress, multiple dynamic exchanges can occur, endowing the material with excellent self-healing properties, recyclability, and mechanical toughness, while maintaining good thermal and chemical stability.

[0010] In some other embodiments, the solvent is ethanol or methanol; the condensation reaction is carried out at a temperature of 75-85°C for 7-9 hours. Drying is performed under vacuum at 35-45℃ for 20-30 hours.

[0011] Specifically, the condensation reaction is carried out at a temperature of 75, 80, or 85°C for 7, 8, or 9 hours; drying is carried out under vacuum at 35, 40, or 45°C for 20, 24, or 30 hours. More specifically, the solvent is ethanol; the condensation reaction is carried out at 80°C for 8 hours; drying is carried out under vacuum at 40°C for 24 hours.

[0012] Using ethanol as a solvent, it does not directly participate in the chemical reaction of the curing agent, and high-purity IDSE can be obtained after standing and separation.

[0013] In some other embodiments, the molar ratio of the imine bond in the dual dynamic bond curing agent to the epoxy group in the epoxy resin is 1:(2-2.2). Specifically, the molar ratio of imine bonds in the dual-dynamic-bond curing agent to epoxy groups in the epoxy resin is 1:2, 1:2.1, or 1:2.2. More specifically, the molar ratio of imine bonds in the dual-dynamic-bond curing agent to epoxy groups in the epoxy resin is 1:2. Under this ratio, the amino groups provided by IDSE react completely with the epoxy groups of E51, ensuring the formation of the dual-dynamic-bond network. The imine bonds, as dynamic bonds, can undergo reversible exchange under mild conditions (such as heating or the involvement of water molecules), endowing the material with self-healing and recyclable properties. Simultaneously, the nitrogen atoms in the imine bonds act as nucleophiles, efficiently catalyzing the ring-opening of epoxy groups to form stable CN covalent bonds, constructing a permanent cross-linked network. This approach maintains the excellent mechanical properties and thermal stability of traditional epoxy resins while achieving the material's repairability and reprocessability.

[0014] The epoxy resin is one or more of epoxy resin E51, epoxy resin E4 type and epoxy resin E42.

[0015] In some other embodiments, the epoxy resin is epoxy resin E51; The ring-opening addition reaction is carried out at a temperature of 75-85℃ for 1.2-1.5 hours.

[0016] Specifically, the ring-opening addition reaction is carried out at a temperature of 75, 80 or 85 °C for a time of 1.5, 1.2 or 1.0 h.

[0017] In some other embodiments, before adding the dual-dynamic bond curing agent to the epoxy resin, the epoxy resin is first heated to 55-65°C, and then the dual-dynamic bond curing agent is added in batches. Heating the epoxy resin at 60°C reduces its viscosity, improves its fluidity, and facilitates uniform dispersion of the curing agent. Adding it in batches allows for the gradual release of heat of reaction, resulting in a stable temperature rise in the system and ensuring thorough mixing and uniform reaction between the curing agent and the epoxy resin, forming a dense, defect-free cross-linked network. Simultaneously, it avoids side reactions or curing agent decomposition caused by excessively high temperatures.

[0018] In some other embodiments, the gradient temperature curing is performed by first curing at 75-85°C for 1.5-2.5 h, then increasing the temperature to 115-125°C for 1.5-2.5 h, and then increasing the temperature to 145-155°C for 1.5-2.5 h, with a heating rate of 5-10°C / min for each stage.

[0019] Specifically, the gradient temperature curing process involves first curing at 80℃ for 2 hours, then increasing the temperature to 120℃ for 2 hours, and finally increasing it to 150℃ for 2 hours. By gradually increasing the temperature and releasing the heat of curing reaction step by step, the agglomeration caused by the sudden and rapid increase in system temperature is effectively avoided, significantly reducing the internal thermal stress and defect density of the material. At the same time, the staged curing process is conducive to the full extension and orderly arrangement of molecular chains, constructing a denser and more regular three-dimensional cross-linked network, ultimately obtaining a high-performance material with synergistic optimization of mechanical properties, thermal stability, and structural integrity.

[0020] Secondly, the present invention provides an epoxy resin containing dual dynamic bond synergistic exchange, prepared by the method for preparing the epoxy resin with dual dynamic bond synergistic exchange described in the first aspect. This material integrates highly efficient room temperature self-healing, controllable degradation, and good mechanical and insulating properties.

[0021] In some other embodiments, the epoxy resin with dual dynamic bond synergistic exchange contains both imine and disulfide bonds in its structure. The synergistic mechanism of disulfide and imine bonds forming in the epoxy resin system in this invention essentially constructs a multi-mode dynamic interconnected network with complementary functions and hierarchical response characteristics. In this network, the two types of dynamic chemical bonds work together temporally and mechanistically to enhance the material's self-adaptive and repair capabilities. The imine bond, as a rapidly responding dynamic unit in the system, preferentially breaks upon exposure to external stimuli (such as acidic environments or moisture), effectively reducing the crosslinking density and modulus of the crack interface region, thereby promoting chain segment movement, creating kinetic conditions for the subsequent repair process, and widening the healing window. The disulfide bond, as a high-strength dynamic connection point in the network, plays a crucial role in structural consolidation after the imine bond completes its initial "softening," achieving chemical reconnection and substantial recovery of mechanical properties at the crack interface through its strong bond energy and efficient metathesis or free radical recombination mechanism. This molecular-level synergistic design enables epoxy resin materials to maintain high mechanical strength while also possessing efficient self-healing properties, multi-stimulus response capabilities, and good recyclability and reprocessing potential, representing a significant advancement in the integration of structure and function in dynamic covalent polymers.

[0022] Thirdly, the present invention provides the application of the epoxy resin with dual dynamic bond co-exchange described in the second aspect in electronic packaging, electrical insulation, coatings, adhesives and power equipment.

[0023] The beneficial effects of this invention are: (1) This invention is the first to design and synthesize an IDSE curing agent that combines imine and disulfide bonds, achieved through a simple condensation reaction. The molecular structure simultaneously contains amino groups that can react with epoxy groups, as well as imine and disulfide bonds that can undergo dynamic exchange, providing key raw materials for constructing a dual dynamic crosslinking network. Through a stepped temperature curing process, the reaction rate and network structure are precisely controlled, avoiding burst polymerization, reducing internal thermal stress and defect density of the material, and ensuring the stability and repeatability of the material properties.

[0024] (2) Imine bonds and disulfide bonds have the following synergistic effects in epoxy resin systems: Imine bonds, as fast-response units, break preferentially under mild conditions, reducing the crosslinking density of the crack interface and creating kinetic conditions for repair; Disulfide bonds, as high-strength dynamic connection points, subsequently achieve chemical reconnection and mechanical property recovery of the crack interface through metathesis or free radical recombination, forming a multi-mode dynamic network with complementary functions and hierarchical response.

[0025] (3) The prepared material maintains high mechanical strength while also having high efficiency room temperature self-healing performance (significantly improved self-healing efficiency), multi-stimulus response capability (multi-stimulus response such as heat, moisture, reducing agent, etc.), good recyclability and reprocessing potential, as well as excellent electrical insulation performance, which meets the application needs of electronic packaging, power equipment and other fields. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is the Fourier transform infrared spectrum of IDSE, the dual dynamic bond curing agent in Example 1 of the present invention. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Some of the reagents and instruments used are as follows: Reagents: Terephthalaldehyde (analytical grade, Yuanye Biotechnology), 4-aminophenyl disulfide (analytical grade, Anaiji Chemical), epoxy resin E51 (industrial grade, Lanxing New Materials), aniline, ethylenediamine, anhydrous ethanol, tetrahydrofuran (THF), hydrochloric acid, etc., were all analytical grade reagents. The experimental water was deionized water.

[0029] Instruments and equipment: Nuclear magnetic resonance spectrometer (NMR, Bruker AVANCE NEO 400 MHz), Fourier transform infrared spectrometer (FT-IR, Thermo Scientific Nicolet iS20), thermogravimetric analyzer (TGA, TA Instruments Q50), differential scanning calorimeter (DSC, TA Instruments Q200), dynamic thermomechanical analyzer (DMA, TA Instruments Q800), universal testing machine (Instron 5967), broadband dielectric spectrometer (Novocontrol Concept 80).

[0030] As mentioned earlier, current self-healing epoxy resins generally suffer from problems such as limited dynamic functions, poor performance synergy, non-integrated molecular design, insufficient sustainability (non-recyclable), and limited intelligent enhancement of high-end electrical insulation. This invention, through ingenious molecular design, enables different dynamic bonds to achieve functional complementarity and synergistic effects under varying reaction conditions and exchange rates, thereby preparing a multifunctional integrated material with superior overall performance.

[0031] The following is a further explanation with reference to specific embodiments: Example 1 This embodiment provides an epoxy resin containing dual dynamic bond synergistic exchange and its preparation method, specifically including the following steps: (1) The synthetic route of the double dynamic bond curing agent IDSE is as follows: ; Equimolar amounts of terephthalaldehyde and 2,2'-diaminodiphenyl disulfide were weighed and placed in a round-bottom flask. Anhydrous ethanol was added as a solvent, and a reflux condenser was installed. The mixture was then refluxed with magnetic stirring in an oil bath at 80 °C for 6 h. During the reaction, the solution gradually turned pale yellow. After the reaction was completed, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The reaction mixture was placed in a refrigerator at 4 °C and allowed to stand overnight, resulting in the precipitation of yellow flaky crystals. The crystals were filtered and washed three times with a small amount of pre-cooled anhydrous ethanol. The product was collected and dried in a vacuum drying oven at 40 °C for 24 h to obtain a pale yellow powdery solid, which was the target curing agent IDSE.

[0032] The reaction mixture is left to stand in the refrigerator overnight. The solution becomes a mixture of anhydrous ethanol and the curing agent IDSE. Anhydrous ethanol is used as a washing agent and will not directly participate in the chemical reaction with the curing agent. After standing overnight, a solid-liquid separation state is formed. At this time, a vacuum filtration operation is performed using a vacuum filtration flask with a suitable Buchner funnel and filter paper of the corresponding diameter. Repeat the vacuum filtration 5-8 times to obtain IDSE with a high purification rate.

[0033] ¹H NMR data of curing agent IDSE 1 ¹H NMR (400 MHz, DMSO-d6) δ: 8.35 (s, 2H, -CH=N-), 7.80–8.00 (m, 4H, Ar-H from terephthalaldehyde moiety), 7.20–7.50 (m, 8H, Ar-H from 4-aminophenyl disulfide moiety); no matrix peaks were observed (δ≈10.10 ppm), confirming the complete aldehyde-amine condensation reaction.

[0034] ¹³C NMR data of the curing agent IDSE (based on structural derivation and literature reference): ¹³C NMR (100 MHz, DMSO-d6) δ: 162.5 (s, 2C, -C=N-), 145.3 (s, 4C, Ar-C adjacent to SS bonds in 4-aminophenyl disulfide), 134.8 (s, 2C, Ar-C adjacent to -CH=N- interephthalaldehyde moiety), 130.2 (s, 4C, Ar-C in terephthalaldehyde moiety), 128.6 (s, 4C, Ar-C in 4-aminophenyl disulfide moiety), 121.8 (s, 4C, Ar-C in 4-aminophenyl disulfide moiety); no aldehyde-based carbon peak (δ≈192 ppm), further verifying the successful synthesis of IDSE. (2) The preparation method of epoxy resin containing double dynamic bond co-exchange is as follows: The curing agent IDSE synthesized in step (1) and epoxy resin E51 were weighed at a molar ratio of imine bonds to epoxy groups of 1:2 (this ratio ensures complete reaction between the amino groups provided by IDSE and the epoxy groups of E51 to guarantee the formation of a double dynamic bond network). The mixture was placed in a beaker and heated in an oil bath at 80 °C with mechanical stirring until the curing agent was completely dissolved. To increase the fluidity of the epoxy resin, it was first stirred at 60 °C to enhance its fluidity. Then, the curing agent IDSE was added in multiple batches until a uniform, transparent, light yellow liquid was formed. The mixture was then poured into a preheated polytetrafluoroethylene mold. The mold was preheated and sprayed with a release agent to prevent the epoxy resin from falling off due to poor viscosity. Curing was carried out sequentially according to a stepped heating program of 80 °C / 2 h - 120 °C / 2 h - 150 °C / 2 h. After curing, the mixture was cooled to room temperature in the oven and demolded to obtain a transparent, hard, cured epoxy resin, denoted as EP-IDSE.

[0035] ¹H NMR data of EP-IDSE degradation products ¹H NMR (400 MHz, DMSO-d6) δ: 10.03 (s, 2H, -CHO, regenerated from terephthalaldehyde), 7.88 (d, J=8.0 Hz, 4H, Ar-H from regenerated terephthalaldehyde), 7.50-7.63 (m, 8H, Ar-H from 4-aminophenyl disulfide-derived fragments), 5.32-5.50 (br s, 4H, -NH3) + (protonated amine fragments), 6.79-6.91 (m, 4H, Ar-H from amine fragments); the -CH=N- proton peak (δ=8.35 ppm) in the original IDSE almost completely disappeared, confirming the hydrolytic breakage of the imine bond.

[0036] ¹³C NMR data of EP-IDSE degradation products (based on degradation mechanism and structural derivation): ¹³C NMR (100MHz, DMSO-d6) δ: 192.1 (s, 2C, -CHO, regenerated terephthalaldehyde), 146.6 (s, 4C, Ar-C adjacent to -NH3) + The peak values ​​for the amine fragments were 134.5 (s, 2C, Ar-C adjacent to -CHO in regenerated terephthalaldehyde), 130.1 (s, 4C, Ar-C in regenerated terephthalaldehyde), 128.8 (s, 4C, Ar-C in amine fragments), and 122.0 (s, 4C, Ar-C in amine fragments). No -C=N- carbon peak was found in the original IDSE (δ≈162.5 ppm), confirming that the dynamic cross-linked network depolymerized into low-molecular-weight fragments during degradation.

[0037] Example 2 Unlike Example 1, in step (1), the molar ratio of terephthalaldehyde and 2,2'-diaminodiphenyl disulfide is 1.2, while the other steps are the same as in Example 1.

[0038] Example 3 Unlike Example 1, in step (1), the molar ratio of terephthalaldehyde and 2,2'-diaminodiphenyl disulfide is 1.5, while the other steps are the same as in Example 1.

[0039] A comparison of Examples 1-3 revealed that the optimal degradation and insulation properties were achieved when the molar ratio of terephthalaldehyde and 2,2'-diaminodiphenyl disulfide was 1.

[0040] Example 4 1.34 g (10 mmol) of terephthalaldehyde and 4,4'-diaminodiphenyl disulfide (4.34 g, 20 mmol) were weighed and placed in a 250 mL three-necked flask, and 100 mL of anhydrous ethanol was added as solvent. A reflux condenser was installed, and the mixture was magnetically stirred and refluxed in an oil bath at 80 °C for 6 h. During the reaction, the solution gradually turned pale yellow. After naturally cooling to room temperature, it was left to stand overnight in a refrigerator at 4 °C, resulting in the precipitation of yellow flaky crystals. The crystals were filtered, washed three times with a small amount of pre-cooled anhydrous ethanol, and dried in a vacuum oven at 40 °C for 24 h to obtain a light yellow powdery solid, which is the dual dynamic covalent curing agent, denoted as IDSE. The yield was approximately 92%. Nuclear magnetic resonance (NMR) spectroscopy (NMR) was used to analyze the crystals. 1 The structure was confirmed by characterization using 1H NMR and Fourier transform infrared spectroscopy (FT-IR): 1 H NMR (400 MHz, DMSO-d6) δ: 8.35 (s, 2H, -CH=N-), 7.80-8.00 (m, 4H, Ar-H from dialdehyde), 7.20-7.50 (m, 8H, Ar-H from aminodisulfide). FT-IR (KBr, cm -1 ): 1622 (C=Nstretching), 550 (SS stretching); other steps are the same as in Example 1.

[0041] Example 5 1.34 g (10 mmol) of isophthalaldehyde and 4,4'-diaminodiphenyl disulfide (4.34 g, 20 mmol) were weighed and reacted, post-treated, and purified according to the same steps as in Example 1 to obtain a light yellow solid, designated as the dual dynamic covalent curing agent IDSE-M. The yield was approximately 90%. In its ¹H NMR spectrum, the characteristic proton peak of the imine bond (-CH=N-) appeared at δ 8.38 ppm. Due to the meta-substituted benzene ring structure, the aromatic proton peak splitting mode was significantly different from that of IDSE, proving the successful synthesis of a different skeleton structure. Other steps were consistent with Example 1, and the obtained product was labeled as EP-IDSE-M.

[0042] Example 6 4,4'-biphenyl-dicarboxaldehyde (2.10 g, 10 mmol) and 2,2'-diaminodiphenyl disulfide (4.34 g, 20 mmol) were weighed and reacted, post-treated, and purified according to the same steps as in Example 1 to obtain a yellow solid, designated as the dual dynamic covalent curing agent IDSE-B. The yield was approximately 88%. FT-IR spectra showed that, except for 1620 cm⁻¹... -1 The characteristic absorption peak of the imine bond at 550 cm⁻¹ -1 Apart from the weak absorption peak of the nearby disulfide bond, its fingerprint region is significantly different from that of IDSE, indicating the introduction of a larger biphenyl conjugated skeleton; the other steps are consistent with Example 1, and the product is labeled as EP-IDSE-B.

[0043] Comparative Example 1 To investigate the synergistic effect of dual dynamic bonds, unlike Example 1, three curing agents containing single dynamic bonds and corresponding epoxy resins were synthesized, as detailed below: (1) Sample containing only imine bonds (EP-Imine): Curing agent containing imine bonds but not disulfide bonds was synthesized by reacting terephthalaldehyde with aniline. It was then reacted with epoxy resin E51. Other preparation steps were the same as in Example 1. The product was labeled as EP-Imine.

[0044] (2) The sample containing only disulfide bonds (EP-SS) was prepared by directly using 2,2'-diaminodiphenyl disulfide as a curing agent and reacting it with epoxy resin E51. The preparation steps were the same as in Example 1, and the product was labeled as EP-SS.

[0045] (3) Conventional epoxy resin, using ethylenediamine as a curing agent to react with epoxy resin E51, the product is labeled as conventional epoxy resin.

[0046] Comparative Example 2 Unlike Example 1, in step (1), 3-methoxy-4-hydroxybenzaldehyde was used to replace terephthalaldehyde in an equal amount. The other steps were the same as in Example 1.

[0047] Research has found that the imine bond curing agent that reacts with epoxy resin E51 in Example 1 of this invention is obtained by condensation of terephthalaldehyde (a dialdehyde group with an unsubstituted aromatic structure) and aniline. Its molecular backbone is a symmetrical "benzene ring-imine bond-benzene ring" structure with no additional oxygen-containing functional groups.

[0048] The curing agent in Comparative Example 1 is obtained by condensing 3-methoxy-4-hydroxybenzaldehyde (an aromatic structure with a monoaldehyde group and methoxy (-OCH3) and hydroxy (-OH) substituents on the benzene ring) with aniline. This introduces two oxygen-containing functional groups, hydroxyl and methoxy, into the molecule, and the number of aldehyde groups (monoaldehyde groups) differs from the dialdehyde group of the present invention. Correspondingly, the final products obtained after curing the two with epoxy resin E51 also show significant structural differences: the crosslinking structure of the product of the present invention is more symmetrical, while the product of Comparative Example 1, due to the presence of hydroxyl and methoxy groups, exhibits stronger intermolecular hydrogen bonding, higher structural branching, and different crosslinking density and functional group distribution compared to the product of the present invention.

[0049] Comparative Example 3 Unlike Example 1, in step (2), epoxy resin E51 and the curing agent (the curing agent in Example 1) are placed in separate dry containers and allowed to stand at room temperature until the material temperature stabilizes (to avoid affecting the mixing uniformity due to temperature fluctuations). Epoxy resin E51 and the curing agent are added to a mixing container and mechanically stirred (200-300 r / min) for 10-15 min to ensure uniform mixing and obtain a homogeneous resin mixture. The mixed resin mixture is transferred to a vacuum degassing chamber and degassed for 5-10 min at a vacuum of 0.08-0.1 MPa and room temperature to remove air bubbles introduced during stirring. The degassed resin mixture is poured into a pre-treated mold (e.g., coated with a release agent) and then placed in a constant temperature oven for curing: first pre-curing at 60-80℃ for 2-4 h, then heating to 100-120℃ for 4-6 h. After curing, the product is removed from the mold and allowed to cool naturally to room temperature to obtain the cured epoxy resin product. Other steps are the same as in Example 1.

[0050] The study found that in Example 1, the heating rate of each stage of the stepped curing process was controlled at 5-10℃ / min. In the low-temperature stage (40-60℃), the resin and curing agent were allowed to react initially for 2-3 hours. In the medium-temperature stage (80-90℃), the temperature was maintained for 3-4 hours for major cross-linking. Finally, in the high-temperature stage (110-130℃), the reaction was completed in 1-2 hours. Cooling the temperature to below 50℃ before demolding resulted in greater stability. The stepped-cured product exhibited low internal stress, high tensile strength, and high thermal stability (T0). g / T d All of these are better, with fewer bubbles, a smoother surface, and better aging resistance over long-term use; however, conventional curing in Comparative Example 3 is prone to micro-cracks and bubble residue, which reduces mechanical and thermal properties.

[0051] Performance testing 1. The IDSE in Example 1 was characterized by Fourier transform infrared spectroscopy (FT-IR) under the following conditions: scan range 4000–500 cm⁻¹.-1 4 cm resolution -1 The scan was performed 32 times, and the results are shown in Figure 1.

[0052] like Figure 1 As shown, the antisymmetric stretching vibration peak of the acyl group (C=O) in the original IDSE reactant (~1690 cm⁻¹) is... -1 It completely disappeared, and at the same time, it was at 1621 cm. -1 A strong absorption peak appears at 510 cm⁻¹, which corresponds to the stretching vibration characteristic of the imine bond (C=N); in addition, 510 cm⁻¹... -1 The presence of a weak, broad peak nearby matches the stretching vibration signal of the disulfide bond (SS) (the disulfide bond has a low bond energy and weak infrared absorption intensity), further confirming that the molecular structure of IDSE conforms to the design expectations.

[0053] 2. Thermodynamic Performance Analysis The basic thermal properties of EP-IDSE, EP-Imine, and EP-SS materials were evaluated using thermal analysis, and the results are shown in Table 1.

[0054] Table 1 Basic Thermal Properties

[0055] Table 1 shows that the glass transition temperature (T) of EP-IDSE is... g The temperature was 98℃. Comparative Example 1 showed that EP-Imine, containing only imine bonds, and EP-SS, containing only disulfide bonds, had a T... g The temperatures are 120℃ and 80℃ respectively. (EP-IDSE's T...) g The results, falling between the two control samples, indicate that the introduction of dual dynamic bonds modulates the rigidity of the crosslinking network to some extent, giving it both heat resistance and segment mobility, thus providing a basis for dynamic exchange.

[0056] EP-IDSE 5% thermogravimetric temperature (T) under nitrogen atmosphere d，5% The maximum decomposition temperature is 328 ℃. d，max The temperature of 385℃ indicates good thermal stability, sufficient to meet the application temperature requirements of most electrical insulation materials. The decomposition temperature ranges of the three samples, EP-IDSE, EP-SS, and EP-Imine, are similar, indicating that the introduction of dynamic bonds did not significantly impair the thermal stability of the materials.

[0057] 3. Mechanical properties and self-healing properties Tensile test results show that EP-IDSE exhibits good mechanical properties, with tensile strength, Young's modulus and elongation at break reaching 68 MPa, 2.5 GPa and 4.8%, respectively.

[0058] Self-healing performance is the core focus of this study. Macroscopic self-healing experiments showed that after completely cutting the EP-IDSE strip and ensuring close contact of the fracture surfaces, effective reconnection of the fracture surfaces was achieved after 24 hours at room temperature. The healed strip could withstand bending without breaking. Quantitative tensile testing showed that its tensile strength recovered to 62 MPa, with a healing efficiency as high as 91%. Under the same conditions, the healing efficiencies of EP-Imine and EP-SS in Comparative Example 1 were only 25% and 55%, respectively. This indicates that the imine bond and disulfide bond do indeed produce a significant synergistic effect at room temperature, jointly promoting the dynamic reorganization of the damaged interface, thereby achieving highly efficient self-healing.

[0059] When scratches appear on a material surface, the dynamic chemical bonds (imine bonds, disulfide bonds) in the damaged area will break and recombine under mild conditions (such as room temperature or slight heating). Simultaneously, molecular chain segments diffuse towards the scratch through thermal motion / stress-driven processes, ultimately re-crosslinking to form a continuous structure that fills the scratch and restores performance. Scratch repair can be achieved simply by allowing the scratched area to come into close contact (e.g., with slight pressure) and leaving it at room temperature for several hours (or accelerating with slight heating). Materials can achieve self-healing of fracture surfaces at room temperature (91% recovery of tensile strength), and scratches represent a more minor surface damage, making molecular diffusion and bond recombination much easier. Therefore, achieving scratch self-healing is far less challenging than fracture healing.

[0060] The EP-IDSE series materials prepared in this invention represent a significant revolution in the self-healing mechanism of thermosetting resins. Experiments show that, under no external stress and at room temperature (25°C) for 24 hours, the material achieves a tensile strength recovery rate exceeding 89%. This performance signifies a fundamental shift from traditional "externally driven repair" (such as heating or ultraviolet irradiation) to "intelligent self-healing," providing unprecedented convenience and practicality for real-world applications such as on-site maintenance of power equipment and autonomous repair of micro-cracks.

[0061] 4. To further investigate the synergistic mechanism of imine and disulfide bonds, stress relaxation experiments were conducted. The results showed that at 100℃, the stress relaxation rate of EP-IDSE was much faster than that of EP-Imine and EP-SS, and its topological freezing transition temperature (T0) was also significantly lower. v The results were also significantly lower than those of the two control samples. This indicates that in networks with dual dynamic bonds, the ability of chain segments to rearrange and dissipate stress is greatly enhanced.

[0062] The hypothesized synergistic mechanism is as follows: Under thermal or stress stimulation, the more mobile disulfide bonds (-SS-) are exchanged first, triggering a topological reconstruction of the local network. This creates a more favorable spatial conformation and reaction microenvironment for the exchange of neighboring imine bonds, thereby lowering the energy barrier for imine bond exchange. The two complement and promote each other in terms of exchange rate and reaction conditions, jointly constructing a "synergistic exchange system" with a dynamicity far exceeding that of a single dynamic bond network. This is the fundamental reason why EP-IDSE can achieve efficient room-temperature self-healing and rapid degradation.

[0063] 5. Degradation performance study Due to the sensitivity of imine bonds to acid stimulation, EP-IDSE exhibits excellent controllable degradation performance under acidic conditions. When EP-IDSE samples were placed in an HCl-THF solution at pH 2, the samples swelled significantly within 30 minutes and completely degraded into fragments within 2 hours, ultimately resulting in a homogeneous and transparent solution. Degradation kinetics studies showed that the degradation rate was strongly dependent on pH; in solutions with pH values ​​of 1, 2, and 3, the time required for complete degradation was 30 minutes, 2 hours, and over 12 hours, respectively. This pH-responsive controllable degradation characteristic provides a novel and gentle solution for the recycling of epoxy resin products. To facilitate a clear and intuitive presentation of the degradation rate, the degradation rate was characterized using the degradation rate data. The specific degradation principles include the following aspects: (1) Protonation: In an acidic environment, the nitrogen atom (N) in the imine bond is first protonated due to its lone pair electrons (H). + That is, R-CH=NR' + H + → R-CH=N + H-R'; After protonation, the nitrogen atom becomes positively charged, forming an imine salt ion.

[0064] (2) Nucleophilic attack: Water molecules (H2O) act as nucleophiles, attacking the positively charged carbon atom (C) bonded to nitrogen. + ), that is, R-CH=N + HR' + H2O → R-CH(OH)-NH + -R'.

[0065] (3) Proton transfer and breakage: The intermediate undergoes proton transfer, which ultimately leads to the breakage of the carbon-nitrogen bond (CN), i.e., R-CH(OH)-NH. + -R' → R-CHO (aldehyde) + R'-NH3 + (Ammonium salt).

[0066] In (1)-(3), R or R' is independently selected from phenyl or substituted phenyl, wherein the substituent in the substituted phenyl is S, and the substituted position is 2 or 4.

[0067] EP-IDSE exhibits highly efficient and controllable degradation performance in acidic environments due to the pH sensitivity of its imine bond (C=N), as detailed below: Degradation behavior under normal acidic conditions (pH=2): When EP-IDSE samples were immersed in a hydrochloric acid-tetrahydrofuran (HCl-THF) mixed solution at pH=2, the degradation process exhibited distinct stage characteristics. Significant swelling occurred within 30 minutes of immersion, indicating that the acidic medium had rapidly penetrated the material and initiated the hydrolysis of imine bonds. After immersion for 2 hours, the samples were completely degraded into small fragments, ultimately forming a homogeneous and transparent solution with no obvious solid residue, achieving efficient and complete degradation.

[0068] pH dependence of degradation rate: Degradation kinetics studies confirmed that the degradation rate of EP-IDSE is strongly correlated with the ambient pH. Under strongly acidic conditions (pH=1), the protonation and subsequent hydrolysis of imine bonds are significantly accelerated, and the sample can be completely degraded in just 30 minutes. When the pH rises to 3, the reduced acidity leads to a decrease in the activation efficiency of imine bonds, and the time required for complete degradation is extended to more than 12 hours. In neutral or alkaline environments, the hydrolysis of imine bonds is significantly inhibited, and the material maintains structural stability without obvious degradation.

[0069] 6. Evaluation of electrical insulation performance The closed-loop recovery potential of the material was further explored for the degraded solution. After the EP-IDSE sample was completely degraded in an HCl / THF solution at pH=2, the resulting solution was neutralized to neutral with a dilute NaOH aqueous solution, and then most of the THF and water were removed by rotary evaporation, yielding a brownish-yellow viscous mixture rich in degradation products.

[0070] As a potential insulating material, its electrical properties are crucial. Broadband dielectric spectroscopy testing shows that at a 50 Hz power frequency, EP-IDSE has a dielectric constant (ε') of 3.7 and a dielectric loss (tan δ) as low as 0.012, comparable to conventional epoxy insulation materials, indicating that the introduction of the dynamic network did not introduce significant polarization losses. The average voltage of the breakdown field strength test shows that its characteristic breakdown field strength (E0) is... The voltage reaches 38 kV / mm, meeting the requirements of general insulation applications. To better conduct breakdown voltage tests, the epoxy resin sheet should ideally be one millimeter thick to prevent surface flashover during breakdown. It is best to conduct the breakdown test in oil. These results confirm that the self-healing epoxy resin successfully retains its basic electrical properties as an electrical insulation material while achieving dynamic functionality.

[0071] This invention is the first to systematically study the key electrical insulation properties of this type of dual-dynamic epoxy resin, including dielectric properties (dielectric constant, dielectric loss), AC breakdown strength, tracking resistance, and surface charge dissipation behavior. Experimental data fully demonstrate that the introduction of a dual-dynamic crosslinking network not only perfectly preserves the inherent excellent insulation properties of epoxy resin, but also surpasses conventional epoxy resins in key indicators such as breakdown strength uniformity and tracking index (CTI). This discovery fills a gap in the research on the electrical insulation performance of dynamic epoxy resins and provides direct technical basis for the development of next-generation intelligent electrical insulation materials.

[0072] 7. Reusability Evaluation To verify its reusability, this recycled mixture was directly used as part of the curing system and mixed with fresh epoxy resin E51 at a certain mass ratio (recycled material: E51 = 1:4). The mixture was then re-cured according to the same curing procedure (80 ℃ / 2 h - 120 ℃ / 2 h - 150 ℃ / 2 h) to obtain recycled epoxy resin (denoted as r-EP).

[0073] The successful recovery of epoxy resin was confirmed by the following systematic characterization of the recycled epoxy resin (denoted as r-EP): Gel permeation chromatography (GPC) analysis of degradation products: The neutralized degradation solution was analyzed by gel permeation chromatography, and the results showed that its number-average molecular weight (M) was... n The concentration of the polymer is approximately 850 Da, and the distribution is relatively narrow (D < 1.5). This directly confirms that the original three-dimensional cross-linked network has been efficiently depolymerized into low molecular weight oligomers or monomer fragments, providing the necessary fluidity and small molecule reactivity for subsequent reactions.

[0074] Chemical structure verification of the recycled product (FT-IR): Comparing the infrared spectra of the original IDSE curing agent and the recycled mixture, it can be observed that the recycled mixture has a structure at ~1690 cm⁻¹. - A clear carbonyl (C=O) stretching vibration peak reappears at ¹, belonging to the regenerated terephthalaldehyde unit; simultaneously, at ~1620 cm⁻¹... - The characteristic peak of the imine bond (C=N) at position ¹ was significantly weakened. Reanalysis of the proton NMR spectrum of the recovered mixture revealed a peak at the corresponding position, confirming the re-formation of the reactants.

[0075] Performance evaluation of recycled materials: Mechanical property testing of r-EP showed a tensile strength of 55 ± 3 MPa, approximately 81% of the strength of the original EP-IDSE material (68 MPa). Furthermore, after being placed at room temperature for 24 hours, r-EP still exhibited a self-healing efficiency as high as 85%. These data strongly indicate that the recycled product can effectively participate in the construction of new cross-linked networks, and that the recycled material largely restores the core mechanical and self-healing functions of the original material.

[0076] The performance indicators of Examples 1, 5-6 and Comparative Examples 1-2 are shown in Table 2.

[0077] Table 2 Performance Indicators

[0078] In Table 2, " / " indicates that no detection was performed.

[0079] In summary, the tests (GPC, FT-IR, mechanical properties, and self-healing properties) fully demonstrate that the EP-IDSE material based on imine bond acid degradation can not only undergo controlled depolymerization, but its degradation products can also be directly used to regenerate epoxy resins with practical value without complex separation and purification. This work is the first to achieve a complete proof of concept from "degradation" to "regeneration" in this dual dynamic bond epoxy system, elevating degradability to the level of closed-loop recycling, and providing important experimental evidence for the development of truly sustainable thermosetting resins. Upon heating, disulfide bonds (bond energy ~260 kJ / mol) and imine bonds (bond energy ~280 kJ / mol) break before the epoxy backbone (epoxy CC bond energy ~340 kJ / mol), releasing sulfur- and nitrogen-containing small molecular fragments. After the dynamic bonds break, the cross-linking structure of the polymer network is destroyed, and the epoxy backbone (COC, CC bonds) further undergoes thermal decomposition, generating small molecules such as CO2 and hydrocarbons. The residual solids after degradation were collected, and their molecular weight distribution was determined by GPC, while their structure was determined by ¹H-NMR.

[0080] This study successfully designed and synthesized a dual-dynamic covalent bond curing agent (IDSE) possessing both imine and disulfide bonds, and used it to construct a novel biodegradable, self-healing epoxy resin (EP-IDSE). The main conclusions are as follows: The molecular structure of IDSE and the successful construction of the EP-IDSE three-dimensional crosslinked network were confirmed by NMR and FT-IR. The prepared EP-IDSE material maintains good thermal stability (T0). d，5%While maintaining excellent mechanical properties (tensile strength >65 MPa) at temperatures above 320℃, the material exhibits outstanding room-temperature self-healing capabilities with a healing efficiency exceeding 90%, and can achieve rapid and controllable degradation under mild acidic conditions. The material's dielectric constant, dielectric loss, and breakdown field strength all meet the basic requirements for electrical insulation materials, achieving a balance between functionalization and practicality. Through systematic comparative studies and stress relaxation analysis, a synergistic dynamic exchange mechanism between imine and disulfide bonds in an epoxy resin system was clearly revealed for the first time. This mechanism is key to achieving breakthroughs in material performance.

[0081] This invention has developed a series of novel dual-dynamic epoxy resins. These materials have achieved groundbreaking and beneficial effects in terms of room temperature self-healing efficiency, integrity maintenance of electrical insulation properties, and integration of degradation and self-healing functions, solving key problems in existing technologies such as harsh repair conditions, limited functionality, and unclear insulation performance.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an epoxy resin with dual dynamic bond synergistic exchange, characterized in that, Includes the following steps: Aromatic dialdehyde and amino-containing disulfide are added to a solvent for condensation reaction, and the double dynamic bond curing agent is obtained by filtration and drying. The double dynamic bond curing agent is added to epoxy resin for ring-opening addition reaction, and cured by gradient heating and cooled to room temperature to obtain the final product. Wherein, the aromatic dialdehyde is terephthalaldehyde, isophthalaldehyde, 4,4'-biphenyl-dialdehyde or o-phthalaldehyde, and the amino-containing disulfide is 2,2'-diaminodiphenyl disulfide or 4,4'-diaminodiphenyl disulfide.

2. The method for preparing the epoxy resin with dual dynamic bond synergistic exchange according to claim 1, characterized in that, The molar ratio of the aromatic dialdehyde to the amino-containing disulfide is 1:(1-2); The aromatic dialdehyde is terephthalaldehyde, and the amino-containing disulfide is 2,2'-diaminodiphenyl disulfide.

3. The method for preparing the epoxy resin with dual dynamic bond synergistic exchange according to claim 1, characterized in that, The solvent is ethanol or methanol; the condensation reaction temperature is 75-85℃, and the time is 7-9 h; Drying is performed under vacuum at 35-45℃ for 20-30 hours.

4. The method for preparing the epoxy resin with dual dynamic bond synergistic exchange according to claim 1, characterized in that, The molar ratio of imine bonds in the dual dynamic bond curing agent to epoxy groups in the epoxy resin is 1:(2-2.2). The epoxy resin is one or more of epoxy resin E51, epoxy resin E4 type, and epoxy resin E42.

5. The method for preparing the epoxy resin with dual dynamic bond synergistic exchange according to claim 1, characterized in that, The epoxy resin is epoxy resin E51; The ring-opening addition reaction is carried out at a temperature of 75-85℃ for 1.2-1.5 hours.

6. The method for preparing the epoxy resin with dual dynamic bond synergistic exchange according to claim 1, characterized in that, Before adding the dual dynamic bond curing agent to the epoxy resin, the epoxy resin is first heated at 55-65℃, and then the dual dynamic bond curing agent is added in batches.

7. The method for preparing the epoxy resin with dual dynamic bond synergistic exchange according to claim 1, characterized in that, The gradient temperature curing process involves first curing at 75-85℃ for 1.5-2.5 h, then increasing the temperature to 115-125℃ for 1.5-2.5 h, and then increasing the temperature to 145-155℃ for 1.5-2.5 h, with a heating rate of 5-10℃ / min for each stage.

8. An epoxy resin with dual dynamic bond co-exchange prepared by the method of any one of claims 1-7.

9. The epoxy resin with dual dynamic bond synergistic exchange according to claim 8, characterized in that, The structure of epoxy resins with dual dynamic bond co-exchange contains both imine bonds and disulfide bonds.

10. The application of the epoxy resin with dual dynamic bond co-exchange as described in claim 8 or 9 in electronic packaging, electrical insulation, coatings, adhesives and power equipment.

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